This invention relates to products having a low degree of emissivity, and to methods for producing same, and in particular to low emissivity products which also exhibit a high level of moisture vapor permeability.
As pointed out in U.S. Pat. No. 5,231,814 ("U.S. '814"), which is incorporated herein in its entirety by reference, and which is owned by the assignee of this patent application, roof decking typically is formed of structural wood products, such as plywood or oriented strand board ("OSB"). These structural wood products are attached to the structural members of a house by nails or other fastening means.
This roof decking defines the confines of the roof of the house and serves as the substrate for joining the outer protective water-shedding materials, i.e., the tar paper and shingles, which are attached thereto and complete the protective roof assembly.
This roof structure is formed of materials which inherently have minimal thermal insulating and emissivity barrier properties. Therefore, heat transfer through the roof structure from the outdoors to the interior space of, for example, a home, particularly during the summer months, is a problem to homeowner. Either a homeowner undergoes severe discomfort due to elevated temperatures inside the house, or they must pay a high price for installing and operating air conditioning.
Prior to the product described in U.S. '814, the insulative solar or heat emitting properties of a structural roof have undergone limited improvements such as by applying insulative materials to the exterior of the roof decking under the outer protective materials.
Excess heat transfer is generated on a daily basis in the summer months, which penetrates into the interstices of building materials such as sheet rock and insulation causing unwanted elevated temperatures within the interior living space.
Thus, under conventional home construction conditions, the air temperature in attics and ceilings can be raised to about 140 degrees F. or higher.
U.S. '814 addresses certain problems relating to heat transfer. In U.S. '814, a roof structure is fitted with roof decling comprising a sheet of plywood or OSB with a layer of foil material adhered thereto. The foil material comprises a layer of metallic foil such as an aluminum foil material. The foil material covers a roof decking material which in turn is fastened to rafters in a typical roof structure.
The foil material used in U.S. '814 includes a plurality of substantially uniformly distributed perforations which are preformed in the foil material prior to applying of the adhesive, and adhering same to the underlying substrate, i.e., OSB, plywood. The expressed reason for introducing the perforations into the foil material is to permit the passage of moisture between the moisture barrier layer and the roof In this way, it is thought that a significant portion of excess moisture can be released through the perforations located in the foil material thereby permitting the roof decking to "breathe." If a significant portion of the excess moisture is not released, unwanted degradation of the substrate can result.
Moisture can be present due to, for example, water vapor which enters the house during construction (before the roof is put on), or after construction from roof leaks of various types. Unwanted moisture can also result from the cumulative effect of vapor condensation.
Typically, the decking is placed in position with the foil layer facing inwardly toward the attic of the house. The low emissivity foil faces at least one adjacent air space (the attic) to prevent unwanted heat transfer.
A partial sectional view of the roof decking structure is shown in FIG. 1 of U.S. '814. A plan view of the decking structure of FIG. 1 is illustrated in FIG. 2, which shows the perforations in approximately true scale. As shown in FIGS. 2 and 3, the perforations extend only through metallic foil 16 and not through the kraft paper 17 to which the foil is attached. The kraft paper is, in itself, capable of breathing. It is stated in U.S. '814 that kraft paper 17 need not be perforated, although perforations through or partly through the paper are not particularly detrimental. The kraft paper is provided for physical support of the foil during the handling, which precedes attachment of the foil material to the panel structure.
The density of perforations is in the order of 125 per square inch, although perforations in the range of from about 50 to about 160 per square inch are usable. Each perforation is about 0.06 mm or less in diameter.